- 243 - 



fin to be respectively iy'2 and 20-5 cm., whilst in 2 American eels of 63 cm. the same 

 distance was 20 and 23 cm. Consequently, the character mentioned above (distance from 

 the beginning of the dorsal fin to that of the anal in % of the total length) may natur- 

 ally also vary considerably ', even though in most of the American eels it was ca. 9 % 

 or less and in most of the European 10 — 11 '^/o or more. In two Danish eels of 59 cm. 

 from the same locality this dimension was found to be 9*2 "/o and ir2% respectively 

 and in two American eels (also from the same locality) 7'9 and 10'2 % respectively. 



We thus see that though the dorsal tin in A. chrysypa is placed as a rule further 

 back than in A. vulgaris, this character may undergo remarkably great variation within 

 the two species, so that these cannot always be distinguished in single cases by means of 

 the position of the dorsal fin alone. 



b. Young stages 



Even in the youngest known stages, the Leptocephali and the elvers, differences may 

 be detected between specimens from the two sides of the Atlantic. We have seen (p. 163) 

 that the average length of our Leptocephali (Stage 1) was a little over 75 mm. (varying 

 from 60—88 mm.). On the other hand the only two specimens hitherto mentioned of 

 the American Leptocephalns Grassii were only 47 and 49 mm. long (Eigenmann & 

 Kennedy 1. c. p. 84), thus on an average between 2 and 3 cm. shorter than the European- 

 Atlantic specimens ^ And if Eigenmann & Kennedy's figures of Leptocephalus Grassii'^ 

 (see Fig. 3, p. 150) be compared with my photographs of L.brevirostris, it will be seen 

 that there is considerable difference in the form of the head, body and tail. The body 

 is for example, much more pointed both in front and behind, the head flatter and the 

 snout more pointed and longer. Similarly there seem to be many fewer teeth which 

 seem to have a different form from those in L. brevïrostrïs (cf. Fig. 6 A p. 170). 



If we consider further the metamorphosed eel young, we see that there is a difference 

 here also between the European-Atlantic and the American specimens. Reference may be 

 made to the measurements on p. 175 for the lengths of the metamorphosed, well-pig- 

 mented European-Atlantic eel young in summer. If we compare these measurements 

 from different summer months, we see that the minimum length is on an average ca. 

 66 mm. and the smallest specimen hitherto observed was 58 mm. The American material 

 of young eels at my disposal is unfortunately wery small; it consists of 7 speci- 



1 To judge from the position of the anus the American specimen figured was in the same stage of devel- 

 opment as my Stage i. EiGENMANN & KENNEDY give 1. c. p. 84 the following description of L. Grassii. "Body 

 lanceolate, sharp at both ends, deepest at the middle; its depth 5.66 in the length; dorsal beginning about 8 

 segments in front of anus, its rays becoming gradually longer to the caudal, whose rays are about i mm. long; 

 anal similar to the dorsal; pectoral well developed; head sharply conical ,, upper and lower profile equally 

 slanting; eye large, 1.33 in snout, 4. in snout; no pigment cells; segments 65 +40 and 68 -I-40". 



2 According to Grassi and CalandruCCIO, 1. c. p. 13 — 14, the average length of the transparent elvers in 

 the Mediterranean (month?) is 67 mm., whilst the pigmented specimens have an average length of ca. 61 mm. 

 minimum 51 mm,). 



The Leptocephalus stage is certainly also smaller in the Mediterranean than in the Atlantic (varying from 

 60 — 77 mm., in the Atlantic from 60 — 88 mm., average 75'2i mm.). The fact generally known, that the young 

 of the same species of fish before metamorphosis is larger in colder than in warmer waters, seems thus to 

 hold also for the European eel, as the size at metamorphosis in the Mediterranean is a little smaller (ca. 1/2 cm.) 

 than in the Atlantic oif Europe. 



The case seems to be somewhat different with the Leptocephali of the American eel which are much 



31* 



